This invention relates to a novel preparation of triglycerides by rearrangement under the influence of lipase enzymes of rapeseed oils.
The rearrangement of fats and oils under the influence, as rearrangement catalyst, of lipase enzymes in a substantially non-aqueous medium has already been disclosed in our British patent specification N.degree. 1577933. Under the influence of the catalyst, the fatty acid residues of the triglycerides, of which glyceride oils and fats are largely composed, may be rearranged selectively or non-selectively according to the characteristics of the catalyst. Different fatty acid residues may be introduced into a particular triglyceride from another triglyceride or from free fatty acid or alkyl ester thereof included in the reaction medium, which is conducted in liquid phase in the presence or absence of added solvent, which should be water-immiscible, although a small amount of water is introduced with the catalyst and may also be present in the reaction medium to maintain the activity of the catalyst.
It has already been proposed in EP 233,036 to prepare saturated triglycerides containing C.sub.14 and shorter-chain fatty acids by rearrangement with such acids or their alkyl esters of vegetable oils, including rapeseed oil, in the presence of 1,3-selective lipase enzymes as rearrangement catalysts, the oil or the rearranged product being saturated by hydrogenation.
An important aspect of the 1,3-selective lipase rearrangement process is the conversion of cheap vegetable oils containing a high proportion of unsaturated fatty acid residues to symmetrical disaturated triglycerides of stearic and palmitic and higher fatty acids, of which cocoa butter and other expensive vegetable butters are largely composed, to provide fats replicating the melting profiles, for which vegetable butters are highly prized, for use in chocolate, confectionery generally and non-food applications in the pharmaceutical industry.
The source of feedstock for lipase rearrangement processes imposes some limitations on the characteristics of the rearrangement product where the catalyst is selective in action. Thus, a 1,3-selective lipase provides a rearrangement product in which the fatty acids occupying the 1- and 3-positions of its triglycerides are randomly distributed, leaving the 2-position fatty acids unchanged. Where therefore the feedstock consists of highly unsaturated triglycerides, as, for example, in vegetable oils, which are subjected to 1,3-selective rearrangement to obtain symmetrical disaturated triglycerides, these may contain a higher proportion in the 2-position of polyunsaturated fatty acids containing more than one double bond than are found in the corresponding triglycerides of cocoa butter and similar vegetable butters consisting substantially of 2-oleyl triglycerides. It has, however, been proposed to use as feedstock for 1,3-selective rearrangement processes, vegetable oils, e.g. sunflower and safflower oil from seed varieties yielding high oleate oils and thus containing fewer linoleic and more highly unsaturated fatty acids than appears in more familiar varieties. Moreover, whereas palmitic acid, and particularly stearic acid, may be readily obtained from vegetable oils for use in these lipase processes, longer-chain saturated fatty acids, such as arachidic and behenic acids, are less widely available for the preparation of the corresponding 1,3-disaturated triglycerides.